Thanks to everyone for their input on this. I'm pretty sure this trailer has original parts from 2004, due to the fact it was rarely used. So, it may be that it is a caliper problem, especially since I am having difficulty on one side only.

How big of a job is it to replace calipers? I haven't done brakes yet, but have done lots of other things on my vehicles including replaced multiple starters, adjusted valve lifters, etc. It seems that the job should be pretty straightforward but I don't want to assume . . .

Calipers are easy just like on a car. 2 bolts to remove the caliper then remove the brake line from the caliper. Reverse the procedure to reinstall. The harder or messier part is bleeding the brakes. Do a couple searches on this site there should be several good posts on doing this.

Thanks to all the great responses. I've made the decision to do the caliper replacement myself, as it is clear that the starboard side wheel is not turning freely. Thanks, also, bturner, for the recommendation.

I see a couple of different options for the Kodiak 225 caliper, most are around $85 each, depending on finish: